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Pinto: A latched spring actuated robot for jumping and perching

Christopher Y. Xu, Jack Yan, Justin K. Yim

TL;DR

Pinto tackles the challenge of arboreal navigation with a squirrel-sized robot designed to jump from ground to a tree trunk. It introduces a latched parallel-elastic LaMSA mechanism, enabled by twisted-string actuation and carbon-fiber springs, that stores energy separately from the leg stiffness and can switch to a stiff series-elastic mode for precise control. The work demonstrates that latched elastic jumping delivers higher energy than springless or purely series-elastic designs and enables tree perching via microspine grippers, offering a versatile platform for fast, robust forest-ground and trunk traversal. These capabilities open pathways for autonomous arboreal monitoring, potentially improving long-range data collection in challenging forest environments.

Abstract

Arboreal environments challenge current robots but are deftly traversed by many familiar animal locomotors such as squirrels. We present a small, 450 g robot "Pinto" developed for tree-jumping, a behavior seen in squirrels but rarely in legged robots: jumping from the ground onto a vertical tree trunk. We develop a powerful and lightweight latched series-elastic actuator using a twisted string and carbon fiber springs. We consider the effects of scaling down conventional quadrupeds and experimentally show how storing energy in a parallel-elastic fashion using a latch increases jump energy compared to series-elastic or springless strategies. By switching between series and parallel-elastic modes with our latched 5-bar leg mechanism, Pinto executes energetic jumps as well as maintains continuous control during shorter bounding motions. We also develop sprung 2-DoF arms equipped with spined grippers to grasp tree bark for high-speed perching following a jump.

Pinto: A latched spring actuated robot for jumping and perching

TL;DR

Pinto tackles the challenge of arboreal navigation with a squirrel-sized robot designed to jump from ground to a tree trunk. It introduces a latched parallel-elastic LaMSA mechanism, enabled by twisted-string actuation and carbon-fiber springs, that stores energy separately from the leg stiffness and can switch to a stiff series-elastic mode for precise control. The work demonstrates that latched elastic jumping delivers higher energy than springless or purely series-elastic designs and enables tree perching via microspine grippers, offering a versatile platform for fast, robust forest-ground and trunk traversal. These capabilities open pathways for autonomous arboreal monitoring, potentially improving long-range data collection in challenging forest environments.

Abstract

Arboreal environments challenge current robots but are deftly traversed by many familiar animal locomotors such as squirrels. We present a small, 450 g robot "Pinto" developed for tree-jumping, a behavior seen in squirrels but rarely in legged robots: jumping from the ground onto a vertical tree trunk. We develop a powerful and lightweight latched series-elastic actuator using a twisted string and carbon fiber springs. We consider the effects of scaling down conventional quadrupeds and experimentally show how storing energy in a parallel-elastic fashion using a latch increases jump energy compared to series-elastic or springless strategies. By switching between series and parallel-elastic modes with our latched 5-bar leg mechanism, Pinto executes energetic jumps as well as maintains continuous control during shorter bounding motions. We also develop sprung 2-DoF arms equipped with spined grippers to grasp tree bark for high-speed perching following a jump.
Paper Structure (14 sections, 11 figures, 1 table)

This paper contains 14 sections, 11 figures, 1 table.

Table of Contents

  1. Introduction
  2. Background
  3. Methods
  4. System overview
  5. 2 DoF Latched Leg
  6. Front legs and grippers
  7. Self-righting
  8. Electrical system
  9. Experiments
  10. Energy and time
  11. Tree jumping
  12. Other behaviors
  13. Discussion
  14. Acknowledgements

Figures (11)

  • Figure 1: Pinto, a squirrel-sized robot that can jump onto a tree trunk. Video: https://youtu.be/-q4JTjmDX6k
  • Figure 2: A squirrel demonstrating stages of a tree-jump maneuver.
  • Figure 3: Diagram of Pinto. In the self-righting configuration (bottom), Pinto extends its arms forward to fit within the circular profile of its roll cage.
  • Figure 4: Time sequence of a latched jump: latches (shown in yellow) switch the system between parallel-elastic and series-elastic actuation modes. The link shapes shown here are simplified for visualization. On the robot, each link is modified for strength and denser packaging.
  • Figure 5: Experimentally measured torque vs. compression angle for one spring plotted in black and simulated torque exerted by the spring at various ratios of link length plotted in color, generated by varying $L_2$ while keeping $L_1$ and the carbon fiber strip parameters constant.
  • ...and 6 more figures